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Monday, August 24, 2009

ROOF RAT - NORWAY RAT

RangeRoof rats range along the lower half of the East Coast and throughout the Gulf States upward into Arkansas. They also exist all along the Pacific Coast and are found on the Hawaiian Islands (Fig. 2). The roof rat is more at home in warm climates, and apparently less adaptable, than the Norway rat, which is why it has not spread throughout the country. Its worldwide geographic distribution suggests that it is much more suited to tropical and semitropical climates. In rare instances, isolated populations are found in areas not within their normal distribution range in the United States. Most of the states in the US interior are free of roof rats, but isolated infestations, probably stemming from infested cargo shipments, can occur.HabitatRoof rats are more aerial than Norway rats in their habitat selection and often live in trees or on vine-covered fences. Landscaped residential or industrial areas provide good habitat, as does riparian vegetation of riverbanks and streams. Parks with natural and artificial ponds, or reservoirs may also be infested. Roof rats will often move into sugarcane and citrus groves. They are sometimes found living in rice fields or around poultry or other farm buildings as well as in industrial sites where food and shelter are available.Roof rats frequently enter buildings from the roof or from accesses near overhead utility lines, which they use to travel from area to area. They are often found living on the second floor of a warehouse in which Norway rats occupy the first or basement floor. Once established, they readily breed and thrive within buildings, just as Norway rats do. They have also been found living in sewer systems, but this is not common.

Rat SignThe nature of damage to outdoor vegetation can often provide clues as to whether it is caused by the roof or Norway rat. Other rat signs may also assist, but be aware that both species may be present. Setting a trap to collect a few specimens may be the only sure way to identify the rat or rats involved. Out-of-doors, roof rats may be present in low to moderate numbers with little sign in the way of tracks or droppings or runs and burrows.There is less tendency to see droppings, urine, or tracks on the floor in buildings because rats may live overhead between floors, above false ceilings, or in utility spaces, and venture down to feed or obtain food. In food-storage facilities, the most prominent sign may be smudge marks, the result of oil and dirt rubbing off of their fur as they travel along their aerial routes.The adequate inspection of a large facility for the presence and location of roof rats often requires a nighttime search when the facility is normally shut down. Use a powerful flashlight to spot rats and to determine travel routes for the best locations to set baits and traps. Sounds in the attic are often the first indication of the presence of roof rats in a residence. When everyone is asleep and the house is quiet, the rats can be heard scurrying about.

Habitat Modification and SanitationThe elimination of food and water through good warehouse sanitation can do much to reduce rodent infestation. Store pet food in sealed containers and do not leave it out at night. Use proper garbage and refuse disposal containers and implement exterior sanitation programs. Emphasis should be placed on the removal of as much harborage as is practical. For further information see Norway Rats.Dense shrubbery, vine-covered trees and fences, and vine ground cover make ideal harborage for roof rats. Severe pruning and/or removal of certain ornamentals are often required to obtain a degree of lasting rat control. Remove preharvest fruits or nuts that drop in backyards. Strip and destroy all unwanted fruit when the harvest period is over.In tree crops, some cultural practices can be helpful. When practical, remove extraneous vegetation adjacent to the crop that may provide shelter for rats. Citrus trees, having very low hanging skirts, are more prone to damage because they provide rats with protection. Prune to raise the skirts and remove any nests constructed in the trees. A vegetation-free margin around the grove will slow rat invasions because rats are more susceptible to predation when crossing unfamiliar open areas.